BAG family molecular chaperone regulator 3 (BAG3) (BAG3)

BAG3 is a multifunctional co-chaperone protein that plays a critical role in cellular protein quality control by maintaining protein homeostasis through interaction with heat shock proteins, particularly Hsp70 and HSPB8. As a nucleotide exchange factor, BAG3 regulates the ATPase cycle of Hsp70 to facilitate the refolding or degradation of misfolded proteins through both proteasomal and autophagy-lysosomal pathways, a process known as chaperone-assisted selective autophagy (CASA). BAG3 is particularly important in cardiac and skeletal muscle, where it localizes to the sarcomeric Z-disk and maintains myofibril integrity under mechanical and oxidative stress. Mutations in the BAG3 gene have been associated with inherited and sporadic dilated cardiomyopathy and myofibrillar myopathy, making it a therapeutic target of interest for cardiac disease. While some BAG3 variants appear protective against dilated cardiomyopathy, loss-of-function mutations impair contractile function and increase vulnerability to cardiotoxicity from proteasome inhibitors used in cancer therapy. This makes BAG3 an important consideration for evaluating protein quality control pathways as potential therapeutic targets and for understanding susceptibility factors in cardiac drug toxicity.

Other names

Bcl2-associated athanogene 3BAG family molecular chaperone regulator 3Co-chaperone BAG3

Functions as a nucleotide exchange factor that facilitates ADP to ATP exchange in Hsp70, promoting substrate release. Binds to Hsp70 at its nucleotide binding domain to regulate the ATPase cycle. Interacts with HSPB8 and other small heat shock proteins to target misfolded proteins for degradation. Coordinates assembly of the CASA complex for selective autophagy of damaged proteins. Balances protein synthesis and degradation under mechanical stress.